This invention relates to the treatment of water wells and the procedure used in the treatment of water recycled through the well and the gravel pack. The procedure includes recirculating water and at least one additive through the well and a portion of the gravel pack. For example, water containing a sequesterant and then a biocide to effectively clean or otherwise treat the well and the gravel pack may be recirculated for a selected treatment period.
Water wells may become clogged with the formation of various metals, scaling carbonates, usually calcium or magnesium carbonates, as well as iron and various other metal oxides and hydroxides. The clogging or incrustation of the well screens and gravel pack reduces the production or capacity of the well, and attempts to treat these wells with different chemicals, including acids, to bring the carbonates, slime, manganese oxides and iron oxides which generally accumulate under control have not been very successful. Many wells become clogged or impede the flow of water by the formation of bacterial slimes. The bacterial slimes, together with other materials, including metal oxides, clays and various chemical precipitates, interfere with the flow of the water. Therefore, in the production of water from a subterranean formation, it is necessary that the well casing and the gravel pack be kept free of such materials. For example, after completion of the well, plugging or partial plugging of the perforations in the well casing will result due to the formation of scale and bacterial blockage.
Heretofore, in order to avoid these problems, the wells were cleaned by introducing into the well solutions containing chlorine-containing compounds in order to kill the bacteria. The prior art teaches various methods of cleaning wells blocked by bacterial slimes, algae, and the like by incorporating a biocide such as sodium hypochlorite together with acid treatments which open the blockage by chemical action. Presently, there is no good proven method for cleaning water wells and keeping such wells open for extended periods of time. Treating water wells and well screens or perforations with acids has been effective particularly for the removal of scale and metal oxides. However, the use of acids has several disadvantages, especially if the formation is particularly subject to rapid formation of scale. In subterranean formations, for example, the water contains various soluble carbonates and bicarbonates of calcium and other polyvalent cations such as barium, magnesium, iron and the like, which form insoluble compounds, which tend to precipitate at the points where the pressure in the formation is reduced and the pH rises. These reduced pressure areas are adjacent to the well or in the perforations of the well casing, and therefore the production of the water is substantially restricted due to the formation of scale, slime, and the like. Acid use can also severely damage the pump, destroy sacrificial anodes used to protect the pump from corrosion, and also may present a difficult, hazardous storage, handling, and disposal problem.